Donald Nicholson — the Leeds medical school biochemist who mapped human metabolic pathways — has died, writes Jon Volger in The Guardian. He was 96. Nicholson detailed the interactions between enzymes and metabolites in the body, in various bodily functions and in disease, Vogler says. Before he started his work, only about 20 pathways had been charted. In 1955, Nicholson drew the first combined map of these pathways to determine how they interact.